In general, a liquid photo-curable resin composition is widely used as a coating agent (especially a hard coating agent), photoresist or dental material. In recent years, special attention has been paid to a method for producing a three-dimensional object from the photo-curable resin composition by optical stereolithography based on data input into 3-D CAD. As for optical stereolithography technology, JP-A 56-144478 discloses an optical stereolithography for producing a three-dimensional object, which comprises repeating the steps of supplying a liquid photo-curable resin with a required amount of controlled light energy to cure the resin in the form of a thin layer, further supplying a liquid photo-curable resin on the top of the cured layer, and exposing the resin to light under control to cure it into a thin layer to be laminated on the cured layer; and its fundamental practical application method is proposed in JP-A 60-247515. Since then, a large number of proposals on optical stereolithography have been made. Furthermore, JP-A 62-35966, JP-A 1-204915, JP-A 2-113925, JP-A 2-145616, JP-A 2-153722, JP-A 3-15520, JP-A 3-21432 and JP-A 3-41126 disclose techniques for optical stereolithography.
As a typical method for optically producing a three-dimensional object, a method is generally and widely employed that comprises selectively irradiating a liquid surface of a liquid photo-curable resin composition contained in a container with ultraviolet laser light under the control by a computer to cure it to a predetermined thickness so that a desired pattern can be obtained, then supplying a liquid resin composition in an amount enough to form one layer onto the cured layer, irradiating it with ultraviolet laser light likewise to cure it so as to form a cured layer to be laminated continuously, and repeating this lamination steps to obtain a three-dimensional object having a final shape. Since this method makes it possible to produce a three-dimensional object having a very complex shape with ease and in a relatively short period of time, it has recently been attracting much attention.
As the photo-curable resin composition used as a coating agent, photoresist or dental material, there are used those obtained by adding a photopolymerization initiator to a curable resin such as an unsaturated polyester, epoxy (meth)acrylate, urethane (meth)acrylate or (meth)acrylate monomer.
The photo-curable resin composition to be used in optical stereolithography is a composition comprising at least one photopolymerizable compound such as a photopolymerizable modified (poly)urethane (meth)acrylate compound, oligoester acrylate compound, epoxy acrylate compound, epoxy compound, polyimide compound, aminoalkyd compound or vinyl ether compound as an essential ingredient and a photopolymerization initiator. JP-A 1-204915, JP-A 1-213304, JP-A 2-28261, JP-A 2-75617, JP-A 2-145616, JP-A 3-104626, JP-A 3-114732 and JP-A 3-114733 disclose improved arts therefor.
The photo-curable resin composition to be used in optical stereolithography must be a low-viscosity liquid and have small volume shrinkage at the time of curing from the viewpoint of handling properties, shaping speed and shaping accuracy and it must be able to give a three-dimensional object having excellent mechanical properties when photo-cured. Along with the increased demand and expanded application of three-dimensional objects formed by optical stereolithography in recent years, three-dimensional objects have been demanded to have excellent heat resistance with a high heat distortion temperature, high rigidity, and excellent heat dimensional stability with a small thermal expansion coefficient and a small dimensional change regardless of temperature change, in addition to the above properties. For example, three-dimensional objects by optical stereolithography that are used in the design of a complex heating medium circuit or for the analysis of the behavior of a heating medium having a complex structure are required to have small volume shrinkage at the time of photo-curing, a high heat distortion temperature, and rigidity and heat dimensional stability.
Therefore, for obtaining a three-dimensional object having improved heat resistance by optical stereolithography, there have been studied a method in which a benzene ring is introduced into the molecule of a photo-curable resin, a method in which the cross-linking density of a photo-curable material is increased, and the like. Even in these methods, the heat distortion temperature measured under high load is around 70 to 80.degree. C. at the best and the heat resistance is not sufficient.
Furthermore, when the heat resistance of an photo-cured product is to be improved, the volume shrinkage at the time of curing becomes large with the result of a reduction in dimensional accuracy. Therefore, a photo-curable resin composition has not yet been obtained that has both improved heat resistance and reduced volume shrinkage at the time of curing.
In general, the heat resistance is expected to be improved when the cross-linking density of a photo-curable resin composition is increased. An increase in cross-linking density, however, induces a growth in volume shrinkage at the time of curing. That is, the improvement of heat resistance and the reduction of volume shrinkage at the time of curing conflict with each other. Therefore, there has been desired a three-dimensional object by optical stereolithography having excellent heat resistance and small volume shrinkage at the time of curing, breaking through such conflicting relationship between them.
A conventional three-dimensional object formed by optical stereolithography generally has a linear thermal expansion coefficient of 4.times.10.sup.-5 cm/cm/.degree. C. or more, and a three-dimensional object by optical stereolithography having a small thermal expansion coefficient, for example, a linear thermal expansion coefficient of 3.times.10.sup.-5 cm/cm/.degree. C. or less, like that of filler reinforced super engineering plastics (a glass fiber reinforced polyamide-imide resin or the like, for example) has not been obtained yet. Therefore, in consideration of the above situation, a three-dimensional object by optical stereolithography has been desired that has a low thermal expansion coefficient and a small dimensional change even at change of temperature.
Then, the present inventors have found and proposed in Japanese Patent No. 2554443 and JP-A 8-20620 that a three-dimensional object by optical stereolithography having excellent dimensional accuracy with small volume shrinkage at the time of curing, excellent mechanical properties, and excellent heat resistance with a high heat distortion temperature can be obtained when a liquid photo-curable resin composition is blended with a specific filler and the blend is subjected to optical stereolithography.